This invention pertains to the application of a storage device (such as a disk drive, or flash memory, or holographic memory, or any type of data storage) and its use in storing and retrieving user data.
Generally, user data comprises both General Purpose (GP) data and data with special requirements, such as error tolerant or streaming (ETS) data. ETS data is either error tolerant, meaning that the data is still usable even with some errors, or streaming, meaning that each block of data follows the next in a “file”-like format, or both. As such, streaming Audio/Visual (AV) data would serve as an example of ETS data. Streaming AV data might come in the form of an MPEG-4 encoded TV program, for example. TV programs can be error tolerant, because the viewers will generally not mind small numbers of errors. Other error tolerant data could include communications between video game consoles, where players will generally not mind occasional errors. General Purpose data might be exemplified by such general system data as that which exists in a file allocation table or a general application file, where even a single-bit error can cause serious problems, and it is not always necessary to stream data at a high rate. GP data is typically reliant on data integrity, whereas ETS data may be more reliant on time of arrival. ETS data may be different than general purpose (GP) data in its relaxed bit error rate (BER) requirement or perhaps other unique aspects. The term BER as used herein refers to a system level “corrected” bit error rate.
ETS data may be more file-like than GP data. As an example of ETS data is an AV data stream. An AV stream can be a stream of HDTV signals for example, including Dolby AC-3 audio. Such AV data is an example of a data-rich, error tolerant stream of ETS data. Generally, an HDTV movie encoded with MPEG-4 AVC compression is expected to operate at a bit rate of 10-30 Mbps. The source may be prone to some errors and the target resilient to some errors as well. AV streams delivered over a network such as Data Over Cable (DOC) are specified by DOCSIS to have a BER of less than 10−8 bits per second. At 10 Mbps, this results in approximately 10 seconds between errors. Disk drives and flash memory systems are designed to provide an uncorrectable error rate of less than 10−14 to 10−15. Disk drives and flash memories are over designed for AV data storage by many orders of magnitude. A target system for an MPEG-4 data stream has built in resilience to some errors. Case studies have shown good MPEG-4 video display quality even when the network decoder delivers no better than 10−6-10−7 post forward error correction (FEC) BER. ETS data allows the storage device to take advantage of certain unique features of the data to format its content at a higher density than GP data.
It is therefore an object of the invention to provide a data storage device with increased storage density for data which is error tolerant or streaming (ETS). It is another object of the invention to provide a method to better align the resources of a data storage device to the requirements of ETS data content. It is a further object of the invention to provide a method to increase the storage density and read throughput rate of ETS data in a storage device with respect to the prior art, and to deliver a corrected BER of better than 10−9 for full quality AV data.